This invention relates to electrophotographic apparatus and, more particularly, to a novel photoconductive member and to a method of making such a member.
The use of an intermediate transfer member in an electrostatographic machine to transfer toner from an imaging member to a receiver (e.g., paper) is well known and is practiced in commercial electrophotographic copiers and printers. A toner image formed on a primary image-forming member (PIFM) is transferred in a first transfer operation to an intermediate transfer member (ITM), and is subsequently transferred in a second transfer operation from the ITM to a receiver. In the second transfer of a toner image from an ITM roller to a receiver, a transfer back-up roller is commonly used behind a paper receiver, a nip being formed to press the receiver to the ITM.
As disclosed by Rimai, et al., in U.S. Pat. No. 5,084,735, and Zaretsky, et al., in U.S. Pat. No. 5,370,961, use of a compliant ITM roller coated by a thick compliant layer and a relatively thin hard overcoat improves the quality of electrostatic toner transfer from an imaging member to a receiver, as compared to a non-compliant intermediate roller. Zaretsky, in U.S. Pat. No. 5,187,526, further discloses that electrostatic transfer can be improved by separately specifying the resistivity of the ITM roller and the transfer back-up roller. Bucks, et al., in U.S. Pat. No. 5,701,567, discloses an ITM roller having electrodes embedded in a compliant blanket to spatially control the applied transfer electric field. Tombs, et al., in U.S. Pat. No. 6,075,965, discloses the use of a compliant ITM roller in conjunction with a paper transport belt in a multi-color electrophotographic machine.
For thermal transfer of toner from a photoconductor to a receiver surface, by Jackson, et al., in U.S. Pat. No. 5,536,609, shows the use of a compliant roller, pad or coating behind a photoconductive belt to assist in the transfer of toner images to a receiving sheet carried by a metal roller. The advantage of the compliant surface behind the photoconductor is that it compresses and widens the nip for good thermal transfer and allows the use of a hard, thermally conductive roller for carrying the receiver paper. Aslam, et al., in U.S. Pat. No. 5,339,146, and Miwa, et al., in U.S. Pat. No. 4,531,825, also suggest an advantage in a compliant surface for a photoconductive member in transferring toner to a heated, hard intermediate transfer member.
The use of a removable endless belt or tubular type of blanket on an intermediate roller has long been practiced in the offset lithographic printing industry, as recently disclosed by Gelinas, in U.S. Pat. No. 5,894,796, wherein the tubular blanket can be made of materials including rubbers and plastics and can be reinforced by an inner layer of aluminum or other metal. As disclosed earlier, for example by Julian, in U.S. Pat. No. 4,144,812, an intermediate lithographic roller comprises a portion having a slightly smaller diameter than the main body of the roller, such that a blanket member can be slid along this narrower portion until it reaches a location where a set of holes located in the roller allow a fluid under pressure, e.g., compressed air, to pass through the holes, thereby stretching the blanket member and allowing the entire blanket member to be slid onto the main body of the roller. After the blanket is located in a suitable position, the source of compressed air or fluid under pressure is turned off, thereby allowing the blanket member to relax to a condition of smaller strain, such strain being sufficient to cause the blanket member to snugly embrace the roller. A sleeve for a printing roller and methods for mounting and dismounting are also disclosed by Hoage et al., in U.S. Pat. No. 4,903,597.
Vrotacoe, et al., in U.S. Pat. No. 5,553,541, discloses a printing blanket, for use in an offset printing press, which includes a seamless tubular elastic layer having compressible microspheres, surrounded by a seamless tubular layer made of a circumferentially inextensible material, and a seamless tubular printing layer over the inextensible layer. It is disclosed that provision of the inextensible layer reduces or eliminates pre-nip and post-nip bulging of the roller when printing an ink image on a receiver sheet, thereby improving image quality by reducing or eliminating ink smearing caused by slippage associated with the formation of bulges in the prior art.
An intermediate transfer roller consisting of a rigid core and a removable, replaceable intermediate transfer blanket has been disclosed by Landa et al., in U.S. Pat. No. 5,335,054, and by Gazit et al., in U.S. Pat. No. 5,745,829, whereby the intermediate transfer blanket is fixedly and replaceably secured and attached to the core. The intermediate transfer blanket, disclosed for use in conjunction with a liquid developer for toning a primary image, consists of a substantially rectangular sheet mechanically held to the core by grippers. The core (or drum) has recesses where the grippers are located. It will be evident from U.S. Pat. Nos. 5,335,054 and 5,745,829 that owing to the presence of the recesses, the entire surface of the intermediate transfer drum cannot be utilized for transfer, which is a disadvantage requiring costly means to maintain a proper orientation of the useful part of the drum when transferring a toner image from a primary imaging member to the intermediate transfer roller, or, when transferring a toner image from the intermediate transfer roller to a receiver. Moreover, the fact that the blanket does not form a continuous covering of the entire core surface, owing to the fact that two of its"" edges are held by grippers, is similarly a disadvantage. Another disadvantage arises because there is inevitably a gap between these edges, so that contamination can become deposited there which can lead to transfer artifacts.
Mammino et al., in U.S. Pat. No. 5,298,956, and Mammino et al., in U.S. Pat. No. 5,409,557, both disclose a reinforced seamless intermediate transfer member that can be in the shape of a belt, sleeve, tube or roll and including a reinforcing member in an endless configuration having filler material and electrical property regulating material on, around or embedded in the reinforcing member. The reinforcing member can be made of metal, synthetic material or fibrous material, and has a tensile modulus ranging from about 400,000 to more than 1,000,000 psi (2.8 to more than 6.9 GPa). The intermediate transfer member has a thickness between 2 mils and about 7 mils, and a bulk resistivity less than about 1012 ohm-cm.
A xerographic printing sleeve mountable on a rigid drum, disclosed by Kuehnle, in U.S. Pat. No. 4,255,508, includes a very thin inorganic photoconductive crystalline compound such as cadmium sulfide coated on a thin metallic sleeve made of a suitable metal, e.g., nickel. The thickness of the photoconductive layer is 200-600 nanometers and is at most of the order of one micrometer. Such a sleeve is not compliant.
An electrostatographic imaging member in the form of a removable replaceable endless imaging belt on a rigid roller is disclosed by Yu et al., in U.S. Pat. No. 5,415,961. The electrostatographic imaging member is placed on the rigid roller and removed from the rigid roller by means involving stretching the endless imaging belt with a pressurized fluid.
An electrostatographic imaging member that includes a photoconductive drum that has inserted therein a compressible sleeve with the composite then being expanded to fit upon a rigid cylindrical core support is disclosed by Swain, in U.S. Pat. No. 5,669,045. The preferred sleeve is a foam that provides substantially no interference fit with the photoconductive drum to facilitate insertion of the sleeve within the drum. However, a relatively large interference fit exists between the rigid core and the sleeve to compress the sleeve as it is expanded by an expandable core. The compression of the sleeve is sufficient to render the electrostatographic imaging member substantially rigid and substantially free from distortion. A problem with an imaging member of the type described by Swain is that the photoconductive drum is not separately removable from the sleeve without also removing the sleeve from the core, thereby subjecting the sleeve to possible damage.
Tombs, et al., in U.S. Pat. No. 5,715,505, and May, et al., in U.S. Pat. No. 5,828,931, both disclose a primary image-forming member (PIFM) roller including a thick compliant blanket layer coated on a core member, the thick compliant blanket surrounded by a relatively thin concentric layer of a photoconductive material. The compliant primary imaging roller provides improved electrostatic transfer of a toner image directly to a receiver member. It is disclosed that the compliant imaging roller can be used bifunctionally, i.e., it can serve also as an intermediate member for electrostatic transfer of a toner image to a receiver. May, et al., in U.S. Pat. No. 5,732,311, discloses a compliant electrographic PIFM roller. Disclosures in U.S. Pat. Nos. 5,715,505; 5,828,931; and 5,732,311 are hereby incorporated by reference.
Tombs, et al., in U.S. Pat. No. 5,715,505, and May, et al., in U.S. Pat. No. 5,828,931, both disclose improvements in the electrostatic transfer of toner images from a photoconductive member to a receiving surface. The photoconductive member has a layer of compliant material having a Young""s modulus less than 5xc3x97107 Pascals and a thin, hard photoconductive layer on the layer of compliant material, preferably of thickness less than 15 micrometers and typically having a Young""s modulus well in excess of 108 Pascals, for example, 1010 Pascals or more. The photoconductive members of these patents provide important advantages in the quality of the transferred images. However, the previously known method of making such photoconductive members has certain drawbacks. May, et al., in U.S. Pat. No. 5,828,93 1, discloses the photoconductive member is made by coating a thin layer of a photoconductive composition on the compliant layer surface of a cylindrical core. A problem encountered in this operation is that the compliant layer materials, which can be, for example, a polyurethane, silicone rubber or other elastomer typically having a low glass transition temperature (Tg). When compliant layer materials are highly cross-linked, they tend to leak residue monomers and to swell in contact with solvents used for coating the photoconductive layer. The compliant layer, therefore, can be damaged by the coating solvent for the photoconductive material. It can also be thermally degraded when the photoconductive layer is heated to evaporate the solvent.
Another drawback of coating a photoconductive layer onto a compliant layer is that the two layers then are adhesively bonded together. Consequently, when the photoconductive layer, after a period of use, becomes worn and needs to be replaced, the entire assembly, including the cylindrical core (which is typically highly toleranced and expensive), the compliant layer and the photoconductive layer must be replaced.
A need exists, therefore, for a compliant photoconductive member and for a method of making it that eliminates the need for coating a photoconductive layer on a compliant layer. A need also exists for a photoconductive member in which the photoconductive layer can be replaced when it becomes worn or at the end of its useful life, with continued use of the core and its"" compliant layer.
The present invention meets these needs by providing a photoconductive member that is a sleeved, compliant, electrostatographic imaging member, useful in electrostatographic color reproduction, and a method for making such a member. The invention includes a method of making such a member, and methods for using the member for color reproduction.
The imaging member of the invention, preferably photoconductive, includes a central member including a substantially rigid cylindrical first substrate or core member, a central member having a compliant layer covering and adhered to the first substrate, and a second substrate in the form of a flexible thin endless tubular belt having coated thereon an imaging structure including one or more thin layers. The second substrate and imaging structure form a sleeve in close-fitting but non-adhesive contact with the compliant layer.
In the method of making a photoconductive imaging member of the invention a compliant backing is made by coating a compliant layer on a first substrate, coating a photoconductive structure including one or more layers on a second substrate, and mounting the coated second substrate in close fitting but non-adhesive contact with the compliant layer of the first substrate.
Methods of using a photoconductive imaging member of the invention include usage as a primary image forming member and usage as a bifunctional photoconductive intermediate transfer member in a color reproduction apparatus.
Advantages obtained by the invention include: preventing the coating solvent used to coat the photoconductive structure from contacting the compliant layer, thereby making a compliant imaging member more reliably and more cheaply, and, providing replacement of the photoconductive structure without the necessity of replacing the compliant layer and its first substrate, thereby lowering cost and reducing downtime.
In accordance with the invention there is provided a photoconductive sleeved primary image-forming member roller for use in an electrophotographic machine comprising a central member including a rigid cylindrical core member and a compliant layer formed on the core member; and a flexible, replaceable, removable, photoconductive sleeve member in the form of an endless tubular belt that surrounds and nonadhesively intimately contacts the central member.